Experimental and modeling investigation of CO2 absorption using sodium hydroxide and sodium carbonate solutions

This work of Thesis is part of the research project CODA (Carbon-negative sODA ash plant), which aims to contrast the CO2 accumulation in the atmosphere with the development of a new sustainable and carbon-negative process for the pilot scale production of sodium carbonate (and bicarbonate) from rock salt brine, renewable energy, and CO2. The absorption rate of CO2 at typical gas power plant flue gas concentration (2% - 10%) with sodium hydroxide, sodium carbonate, and sodium bicarbonate solutions is experimentally studied in a fed-batch system changing the temperature, the mass transfer area, and the concentration of CO2 in the gas phase. The experimental results are compared with the results coming from a mathematical model, it is based on the combination of a few different models already available in the literature. Even if the model takes into account the transport in the gas phase, the evaluation is not accurate; therefore, a CFD simulation could be useful to improve the performance of the model, or some experiments in which the dominant resistance is in the gas phase can be performed to obtain it experimentally. For the solutions with NaOH, there is a good agreement between the constructed model and the experiments, namely the mass transfer coefficient average error is 8.44%. Instead, when a solution of sodium carbonate only and sodium carbonate with bicarbonate is present, the model underestimates the mass transfer coefficient ending up with an error equal to 48.82%, opening the possibility for further studies, in particular the fitting of some kinetics parameters. Additionally, through this model the mass transfer coefficient dependence on the initial solution composition, temperature, mass transfer area, and CO2 concentration in the gas phase is investigated As expected, the increase in the temperature leads to an increase in the mass transfer coefficient. The mass transfer area and the CO2 concentration is not strongly impacting the resulting mass transfer coefficient.